Balancer Circuit

ABSTRACT

An apparatus includes a DC-to-AC converter comprising a first output terminal and a second output terminal. The apparatus also includes a DC-to-DC converter comprising a third output. The DC-to-AC converter is configured to receive a DC input voltage from a DC power source, and to produce a first alternating output voltage at the first output terminal, and a second alternating output voltage at the second output terminal. The DC-to-DC converter is configured receive a DC input voltage from the DC power source, and to step down the DC input voltage at the third output.

RELATED APPLICATIONS

The present application is a continuation of U.S. Non-Provisionalapplication Ser. No. 16/877,942, filed May 19, 2020, which is acontinuation of U.S. Non-Provisional application Ser. No. 15/925,882,filed Mar. 20, 2018, now U.S. Pat. No. 10,700,618, which claims priorityto U.S. provisional application Ser. No. 62/475,452, filed Mar. 23,2017. These applications are hereby incorporated by reference in theirentirety.

BACKGROUND

Some electric power systems in various households and industry may besplit-phase electric power systems. A split-phase power system is a typeof single-phase power system that may comprise two alternating current(AC) voltage lines. The AC voltage lines may have a common neutral line.The AC voltage amplitude and/or root mean square (RMS) value withrespect to the neutral line may be about half of the AC voltageamplitude and/or RMS value between the AC voltage lines, i.e.,line-to-neutral voltage amplitude and/or RMS value may be about half ofthe line-to-line voltage amplitude and/or RMS value. In a split-phasesystem providing power to balanced loads, (i.e., where the loads coupledbetween each AC voltage line and the neutral line are about the same),the sum of the instantaneous currents of the two lines may be aboutzero, i.e., the current flowing through the neutral line may besignificantly smaller than the current flowing through the AC voltagelines.

Other electric power systems may be three-phase electric power systems.A three-phase power system has three power lines, each having analternating current of the same frequency and voltage amplitude and/orRMS value with respect to a neutral line. Each power line has a phaseshift of one third of the period with respect to the other two lines. Ina three-phase system feeding balanced loads, the sum of theinstantaneous currents of the three lines may be about zero.

SUMMARY

The following summary is for illustrative purposes only, and is notintended to limit or constrain the detailed description.

Illustrative embodiments disclosed herein may present systems and/ormethods for a split-phase electrical power system that may powerelectrical loads in the split-phase system.

Illustrative embodiments disclosed herein may present efficient systemsand/or methods for generating from a DC power source the voltage linesand the neutral line for a split-phase electrical power system and athree-phase electrical power system that may power electrical loads.Some embodiments may include a resonant switched capacitor circuit thatmay reduce switching losses and may reduce electromagnetic interference(EMI).

Illustrative embodiments disclosed herein may present systems and/ormethods for reducing the imbalance between groups of loads insplit-phase electrical power system and a three-phase electrical powersystem.

In some embodiments disclosed herein, systems and/or methods presentedmay make the use of an autotransformer superfluous.

Embodiments disclosed herein may include but are not limited to methodsfor dividing an AC signal into two AC signals with half the amplitudeand/or RMS value.

DC-to-AC converters referred to within one or more embodiments mayinclude but are not limited to 2-level or multi-level inverter(s) (e.g.,Neutral point Clamp or flying capacitor inverter) and/ormicroinverter(s).

DC power sources and/or DC sources referred to within one or moreembodiments may include but are not limited to PV generator(s) (e.g. PVcell(s), PV string(s), PV substring(s), PV panel(s), PV array(s) ofpanels and/or PV shingles), fuel cell(s), and/or storage device(s)(e.g., battery(ies), flywheel(s), capacitor(s), supercapacitor(s)).

PV modules referred to within one or more embodiments may include butare not limited to PV generator(s) (e.g. PV cell(s), PV string(s), PVsubstring(s), PV panel(s), PV array(s) of panels and/or PV shingles)and/or PV power module(s) (e.g. PV optimizer(s), PV string optimizer(s),PV combiner box(es), PV converter(s), and/or PV master control unit(s).

DC-to-DC converters referred to within one or more embodiments mayinclude but are not limited to buck converter(s), buck/boostconverter(s), buck+boost converter(s), Cuk converter(s), Flybackconverter(s), forward converter(s), charge-pump converter(s), switchedcapacitor converter(s), and/or resonant switched capacitor converter(s).

Switches referred to within one or more embodiments may include but arenot limited to MOSFET(s), IGBT(s), BJT(s), other transistor(s), and/orrelay(s).

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood with regard to the followingdescription, claims, and drawings. The present disclosure is illustratedby way of example, and not limited by, the accompanying figures in whichlike numerals indicate similar elements.

FIG. 1 is a block diagram of a multi-converter according to illustrativeembodiments.

FIG. 2 a is a block diagram of a multi-converter according toillustrative embodiments.

FIG. 2 b illustrates voltage waveforms that may be provided by amulti-converter according to illustrative embodiments.

FIG. 3 is a block diagram of a multi-converter according to illustrativeembodiments.

FIG. 4 a is part schematic, part block diagram of a multi-converteraccording to illustrative embodiments.

FIG. 4 b illustrates schematic diagrams for a capacitor circuitaccording to illustrative embodiments.

FIG. 5 is part schematic, part block diagram of a multi-converteraccording to illustrative embodiments.

FIG. 6 a is part schematic, part block diagram of an electrical systemhaving a multi-converter according to illustrative embodiments.

FIG. 6 b is a schematic diagram of an electrical system having amulti-converter according to illustrative embodiments.

FIG. 7 illustrates a block diagram of an electrical system having amulti-converter according to illustrative embodiments.

FIG. 8 a illustrates a block diagram of an electrical system having aDC-to-AC converter according to illustrative embodiments.

FIG. 8 b illustrates a block diagram of a switching system according toillustrative embodiments.

FIG. 8 c illustrates a block diagram of a switching system according toillustrative embodiments.

FIG. 8 d illustrates a graphical user interface (GUI) application of aswitching device according to illustrative embodiments.

FIG. 9 illustrates a block diagram of a multi-converter according toillustrative embodiments.

FIG. 10 illustrates a block diagram of a multi-converter according toillustrative embodiments.

FIG. 11 a illustrates a circuit topology of a converter according toillustrative embodiments.

FIG. 11 b illustrates a circuit topology of a converter according toillustrative embodiments.

FIG. 11 c shows three graphs of voltage versus time according toillustrative embodiments.

FIG. 11 d shows two graphs of current versus time according toillustrative embodiments.

FIG. 11 e illustrates a circuit topology of a converter according toillustrative embodiments.

FIGS. 12 a and 12 b show respective step-down DC buck converters withconversion ratios of a half, according to illustrative embodiments.

FIG. 12 c shows graphs of voltages and current versus time according toillustrative embodiments.

FIGS. 13 a and 13 b show respective step-down DC buck converters withconversion ratios of a half, according to illustrative embodiments.

FIG. 13 c shows graphs of voltages and current versus time according toillustrative embodiments.

FIGS. 14 a and 14 b show respective step-down DC buck converters withconversion ratios of a half, according to illustrative embodiments.

FIG. 14 c shows graphs of voltages and current versus time according toillustrative embodiments.

FIGS. 15 a and 15 b show respective step-down DC buck converters withconversion ratios of a half, according to illustrative embodiments.

FIG. 15 c show graphs of voltages and current versus time according toillustrative embodiments.

FIGS. 16 a and 16 b show respective step-down DC buck converters withconversion ratios of a half, according to illustrative embodiments.

FIG. 16 c shows graphs of voltages and current versus time according toillustrative embodiments.

FIG. 17 shows a block diagram of an algorithm to determine a switchingfrequency for a converter described in the above Figures, according toillustrative embodiments.

FIG. 18 a shows a bidirectional AC to AC converter according toillustrative embodiments.

FIG. 18 b shows graphs of voltages and current versus time according toillustrative embodiments.

DETAILED DESCRIPTION

In the following description of various illustrative embodiments,reference is made to the accompanying drawings, which form a parthereof, and in which is shown, by way of illustration, variousembodiments in which aspects of the disclosure may be practiced. It isto be understood that other embodiments may be utilized and structuraland functional modifications may be made, without departing from thescope of the present disclosure.

Reference is now made to FIG. 1 , which illustrates a block diagram of amulti-converter according to illustrative embodiments. Multi-converter102 may comprise terminals 104 a and 104 b and terminals 103 a, 103 band 103 c. Terminals 104 a and 104 b may be coupled to direct-current(DC) source 101. Terminal 103 a and terminal 103 b may provide ACvoltages, and terminal 103 c may provide a DC voltage that maycorrespond to about half of the voltage at terminal 104 a with regard toterminal 104 b. For example, DC source 101 may provide about 400 VDC andterminal 103 c may provide about 200 VDC.

In some embodiments, terminals 103 a and 103 b may provide AC voltagesthat may have opposite phases with respect to terminal 103 c. Forexample, terminal 103 a may provide about sin(ωt) VAC and terminal 103 bmay provide about sin(ωt+π) VAC with respect to terminal 103 c.

Reference is now made to FIG. 2 a , which illustrates a block diagram ofa multi-converter according to illustrative embodiments. Multi-converter207 may comprise direct-current to alternating current (DC-to-AC)converter 202 and DC-to-DC converter 204. DC-to-AC converter 202 andDC-to-DC converter 204 may be configured to receive input power from DCpower source 201. DC-to-AC converter 202 may be configured to output anAC voltage. DC-to-DC converter 204 may be configured to step down the DCvoltage received from DC source 201 by about half (e.g., receive aninput DC voltage of about 340V and output a DC voltage of about 170V). ADC-to-DC converter may comprise two output terminals. In some cases,only one output of DC-to-DC converter may be provided as a referencepoint for the other output terminals. In some embodiments, a secondoutput, not shown in this figure, may provide the same voltage as one ofthe inputs of DC-to-DC converter 204, or a different voltage.

Still referring to FIG. 2 a , the voltage provided at first output 203 amay be an AC voltage, and the voltage provided at second output 203 bmay be an AC voltage with a phase shift of about 180 degrees with regardto the voltage at first output 203 a. The voltage provided at thirdoutput 205 a may be a middle voltage about equal to the midpoint voltagevalue between the voltage provided at first output 203 a and the voltageprovided at second output 203 b. As a numerical example, the secondterminal of DC source 201 may provide a voltage of about 340V withrespect to the first terminal of DC source 201, the voltage provided atfirst output 203 a may be about 170+sin(2πft)V with respect to the firstterminal of DC source 201, the voltage provided at second output 203 bmay be about 170+sin(2πft+π)V with respect to the first terminal of DCsource 201, and the voltage provided at third output 205 a may be about120V with respect to the second terminal of DC source 201, which may beabout the middle voltage between the voltage at the first output 203 aand the voltage at the second output 203 b, and may be also about halfthe voltage provided by DC source 201.

In some embodiments, multi-converter 207 may perform estimation and/ordetermination of an electrical parameter (e.g., voltage, current, and/orpower) at one or more of outputs 203 a, 203 b and 205 a. Estimationand/or determination may be performed, for example, by a directcalculation, probabilistic calculation, measuring, sensing, lookupand/or reception (e.g., via wired or wireless communication) of anestimated or determined value. One or more sensors may be used tomeasure and/or sense the electrical parameters at first output 203 a,second output 203 b and/or third output 205 a. In some embodiments,where measuring electrical parameters may include measuring current, itmay be sufficient to measure and/or sense only two of the currents attwo of the outputs. If there may be a need to determine and/or estimatethe current at the third output that might not be measured, the currentat the third output may be determined and/or estimated according toKirchhoff s circuit laws. For example, the current flowing out of output203 a may be 10 A, the current flowing in output 205 a may be 1 A, andaccording to Kirchhoff's current law the current flowing in 203 b may becalculated to be 9 A. In some embodiments, it may be sufficient todetermine and/or estimate only one electrical parameter. For example, acontroller controlling DC-to-DC converter may measure and/or sense thecurrent at output 205 a and may reduce the current accordingly.

In some embodiments, electrical (e.g., voltage, power and/or current)measurements may be used as feedback parameters for control of DC-to-ACconverter 202 and switching of DC-to-DC converter 204. In someembodiments, measurements may be used for logging data, updating a userinterface and/or feedback for operating a load switching circuit(described below).

In some embodiments, DC-to-DC converter 204 may comprise multiple DCoutputs for various applications (e.g., additional DC levels for amulti-level converter and/or power for one or more DC loads).

Reference is now made to FIG. 2 b , which illustrates voltages that maybe output by a multi-converter (e.g., multi-converter 207 of FIG. 2 a )according to illustrative embodiments. For illustrative purposes, thevoltage at the first terminal of DC source 201 may be denoted as zerovoltage. The voltage at the second terminal of DC source 201 may beV_(DC) with respect to the first terminal of DC source 201. Voltages S1and S2 may represent the voltage at output 203 a and at output 203 b,respectively, with respect to the first terminal of DC source 201.Voltages S1 and S2 may represent AC voltages that may oscillate betweenzero and V_(DC) with respect to the first terminal of DC source 201.Voltage S3 may represent the voltage at output 205 a, which may be abouthalf of V_(DC) with respect to the first terminal of DC source 201.Voltage S4 may represent the voltage at output 203 a with respect tooutput 203 b. Voltage S4 may oscillate in a sinusoidal manner between±V_(DC). Voltage S5 may be a voltage having an amplitude between thevoltage amplitude of output 203 a and the voltage amplitude of output205 a. Voltage S5 may oscillate in a sinusoidal manner or any other typeof a periodic wave between ±½V_(DC). Voltage S6 may be a voltage havingan amplitude between the voltage amplitude of output 203 b and thevoltage amplitude of output 205 a. Voltage S6 may oscillate in aperiodic (e.g., sinusoidal) manner between ±½V_(DC). Voltages S5 and S6may be phase-shifted by about 180 degrees with respect to each other.

Reference is now made to FIG. 3 , which illustrates a block diagram of amulti-converter according to illustrative embodiments. Multi-converter300 may comprise DC-to-DC converter 302 and DC-to-AC converter 303.DC-to-DC converter 302 may be similar to DC-to-DC converter 204 of FIG.2 a . DC-to-AC converter 303 may be similar to DC-to-AC converter 202 ofFIG. 2 a . The input terminals of DC-to-DC converter 302 and of DC-to-ACconverter 303 may be coupled to nodes N31 and N32, which may be coupledto input 301 a and 301 b, respectively. The output terminal of DC-to-DCconverter 302 may be coupled to node N33, which may be coupled to one ofthe inputs of DC-to-AC converter 303 and may be coupled to thirdterminal 306. The outputs of DC-to-AC converter 303 may be coupled tofirst terminal 304 and to second terminal 305.

Still referring to FIG. 3 , in some embodiments, DC-to-AC converter 303may use the voltage that is outputted by DC-to-DC converter 302depending on the converter topology. For example, a neutral pointclamped (NPC) inverter or a different topology of multi-level invertermay use the mid-voltage for harmonic reduction by creating more voltagelevels than a two-level inverter.

In some embodiments, multi-converter 300 may be configured to convert DCpower from one or more PV modules to AC power for a residential orcommercial split-phase electrical system. Multi-converter 300 maycomprise a controller configured for increasing power and/or for maximumpower point tracking (MPPT) and/or impedance matching.

Reference is now made to FIG. 4 a , which is part schematic, part blockdiagram of a multi-converter according to illustrative embodiments.Power source 401 may be coupled to multi-converter 400. Multi-converter400 may be an implementation of multi-converter 300 of FIG. 3 .Multi-converter 400 may comprise resonant switched capacitor circuit(RSCC) 414 and DC-to-AC converter 410. RSCC 414 may be a part of aDC-to-DC converter similar to DC-to-DC converter 302 of FIG. 3 . Theinput terminals of RSCC 414 may be coupled to nodes N41 and N42, whichmay be similar to nodes N31 and N32 of FIG. 3 . Nodes N41 and N42 may becoupled to power source 401. The output of RSCC 414 may be coupled tonode N43, which may be similar to node N33 of FIG. 3 . RSCC 414 may, insome embodiments, be replaced by a different topology of a DC-to-DCconverter, for example, a Buck, Boost, Buck/Boost, Buck+Boost, Flyback,Forward or Cuk converter, etc. Using the topology of RSCC 414 or asimilar topology as a DC-to-DC converter may increase efficiency whenthe desired output of RSCC 414 is about half the input voltage. SignalsC1, C2, C3 and C4 may be configured to control switches 402 . . . 405 ofRSCC 414 to provide at the output of RSCC 414 a voltage of about halfthe input voltage. Signals C1-C4 may be switched between two voltagelevels, each level representing a state of a switch (e.g. “on” and“off”). In some embodiments, RSCC 414 may comprise but are not limitedto four switching modes. During the first mode, switches 402 and 404 maybe “on”. During the second mode, switches 403 and 404 may be “on”.During the third mode, switches 403 and 405 may be “on”. During thefourth mode, switches 402 and 405 may be “on”. A controller (not shownin FIG. 4 a ) providing signals C1-C4 may control the switching betweenmodes and the time interval of one or more modes. In some embodiments,the timing of the switching and the values of inductor 406 and capacitor407 may be designed to realize soft switching operation. The averagevoltage of capacitor 407 may be about half of the input voltage. Otherembodiments may comprise different switching modes that may achievesimilar results. RSCC 414 may comprise capacitor circuit 408. Capacitorcircuit 408 may be designed to reduce the ripple at the output of RSCC414. Some implementations of capacitor circuit 408 may comprise varioustopologies of capacitors and in some embodiments also switches. In someembodiments, each of switches 402, 403, 404, 405 may be implementedusing a plurality of transistors, for example, MOSFETs, IGBTs, BJTs, orother suitable electronic devices.

An RSCC may reduce the power losses and electromagnetic interference(EMI) compared to other DC-to-DC converters. For example, compared to abuck converter, the RSCC may have a smaller inductor because capacitorcircuit 408 may serve for energy storage similar to switched capacitorcircuits. Compared to switched capacitor circuits (SCC), an RSCC mayhave an additional small inductor, such as inductor 406, which maycontribute to soft switching that may reduce switching losses and alsomay contribute to reducing EMI. RSCC control may be based on variousmethods that may have different properties. For example, RSCC controlmay include fixed periodic gate signals, controlling blanking time,switching frequency, duty cycle, and/or phase-shift angle.

Still referring to FIG. 4 a , some output voltages may correspond tovoltages indicated in FIG. 2 b . For example, the voltage at thirdoutput 413 may correspond to voltage S3 of FIG. 2 b . The voltage atfirst output 411 with respect to third output 413 may correspond tovoltage S5. The voltage at second output 412 with respect to thirdoutput 413 may correspond to voltage S6.

Reference is now made to FIG. 4 b , which comprises schematic diagramsfor a capacitor circuit according to illustrative embodiments. TerminalsCC1 and CC2 may be coupled to the outputs of a DC source, terminal CC4may be coupled between switches 403 and 404 of FIG. 4 a , and terminalCC3 may be coupled to the output of RSCC 414. Capacitor circuits 420 a,420 b and 420 c may be possible implementations of capacitor circuit 408of FIG. 4 a . Capacitor circuit 408 may comprise terminals CC1, CC2, CC3and CC4. Capacitor circuit 420 a may comprise capacitors 422 and 421,wherein the first terminal of capacitor 422 may be coupled to terminalCC2, wherein the second terminal of capacitor 421 may be coupled toterminal CC1, and wherein the first terminal of capacitor 421 and thesecond terminal of capacitor 422 may be coupled to each other and toterminals CC3 and CC4.

Still referring to FIG. 4 b , capacitor circuit 420 b may comprisecapacitor 423, switch 424 and switch 425. Terminals CC4 and CC3 may becoupled to each other. Switches 424 and 425 may couple capacitor 423 toterminal CC3 and CC4 and to either terminal CC1 or CC2. Capacitorcircuit 240 b may be operated such that, for a first period of time,switch 425 is controlled to couple the first terminal of capacitor 423to terminal CC4, and switch 424 may be controlled to couple the secondterminal of capacitor 423 to terminal CC1. For a second period of time,switch 425 may be controlled to couple the first terminal of capacitor423 to terminal CC2, and switch 424 may be controlled to couple thesecond terminal of capacitor 423 to terminal CC3. If the voltage atterminal CC4 and CC3 with respect to the voltage at terminal CC2 isabout half of the voltage at terminal CC1 with respect to the voltage atterminal CC2, the voltage over capacitor 423 may be about half of thevoltage at terminal CC1 with respect to the voltage at terminal CC2,with capacitor 423 alternately clamped to the voltage at terminal CC1 orthe voltage at terminal CC2.

For example, switches 425 and 424 may be operated such that for a firstperiod of time, a first terminal of capacitor 423 is coupled (e.g.,connected) to terminal CC2 via switch 425 and a second terminal ofcapacitor 423 is coupled (e.g., connected) to terminal CC3 via switch424, and for a second period of time, the first terminal of capacitor423 is coupled (e.g., connected) to terminal CC4 via switch 425 and thesecond terminal of capacitor 423 is coupled (e.g., connected) toterminal CC1 via switch 424.

Still referring to FIG. 4 b , capacitor circuit 420 c may comprisecapacitor 426, switch 427, switch 428 and switch 429. Switches 427, 428and 429 may couple capacitor 426 to terminal CC3 and CC4 and to eitherterminal CC1 or CC2. Switches 427 and 428 may be switched in acomplementary manner such that the terminals of capacitor 426 might notbe coupled to terminals CC1 and CC2 at the same time, and switch 429 mayselectively connect terminal CC3 to terminal CC4 via switches 427 and/or428. For example, when switch 428 is operated to couple (e.g., connect)the first terminal of capacitor 426 to terminal CC2 and switch 427 isoperated to couple the second terminal of capacitor 426 to terminal CC4,switch 429 may be operated to couple terminal CC3 to the second terminalof capacitor 426.

For example, switches 427, 428 and 429 may be operated such that for afirst period of time, a first terminal of capacitor 426 is coupled(e.g., connected) to terminal CC2 via switch 428 and a second terminalof capacitor 423 is coupled (e.g., connected) to terminal CC4 via switch427 and terminal CC3 is coupled to the second terminal of capacitor 426via switch 429, and for a second period of time, the first terminal ofcapacitor 426 is coupled (e.g., connected) to terminal CC4 via switch428 and the second terminal of capacitor 426 is coupled (e.g.,connected) to terminal CC1 via switch 427 and terminal CC3 is coupled tothe first terminal of capacitor 426 via switch 429.

In some embodiments, each of switches 424, 425, 427, 428 and 429 may beimplemented using a plurality of transistors, for example, MOSFETs,IGBTs, BJTs, or other suitable electronic devices.

Reference is now made to FIG. 5 , which is part schematic, part blockdiagram of an electrical system having a multi-converter according toillustrative embodiments. DC source 501 may be coupled tomulti-converter 500. Multi-converter 500 may comprise block 516 andblock 517. Block 516 may be a resonant switched capacitor circuit thatmay be similar to RSCC 414 of FIG. 4 a , and block 517 may be a DC-to-ACconverter that may be similar to DC-to-AC converter 410 of FIG. 4 a .With respect to block 516, the resonant portion may be provided by theseries connection of inductor 506 and capacitor 507. The seriesconnection of inductor 506 and capacitor 507 may be respectivelyconnected across the point and/or node where switches 502 and 503 areconnected in series and switches 505 and 504 are connected in series.The other ends of switches 502 and 505 connect respectively to thepositive (+) and negative (−) terminals of DC source 501. The other endof switches 503 and 504 connect together to give output 515 ofmulti-converter 500.

With respect to block 517, signals controlling switches 508, 509, 510and 511 may be configured to generate an AC voltage at the output ofblock 517. A series connection of switches 508 and 509 are connectedacross the positive (+) and negative (−) terminals of DC source 501.Similarly, a series connection of switches 510 and 511 are connectedacross the positive (+) and negative (−) terminals of DC source 501. Therespective points and/or nodes of where switches 508 and 509 connectedtogether and where switches 510 and 511 are connected together may beconnected to the input of filter 512. Outputs 513 and 514 may beprovided from the output of filter 512.

In some embodiments, the voltage generated at the output of block 517may be smoothed by filter 512. For example, filter 512 may comprise acircuit (e.g., an LC circuit) designed to reduce the energy at highfrequencies. Block 517 may be referred to as a two-level inverterbecause the outputs of block 517 may be coupled to two voltage levels,the voltage at the first terminal of DC source 501 and the voltage atthe second terminal of DC source 501. Block 517 may be replaced with aDC-to-AC converter that may comprise more DC levels that may be referredto as a multi-level inverter (e.g., a Neutral Point Clamp inverter or aFlying Capacitor inverter). A multi-level converter may use theregulated output of block 516 as an additional DC level.

In some embodiments, the signals controlling switches 508-511 may switchbetween two voltage levels, each level representing a state of a switch(e.g., “on” and “off”). The signals may be generated by an externaldevice and/or a controller, which may be a part that is not shown in theillustration of multi-converter 500. Different types of implementationsof a controller may include a digital signal processor (DSP),micro-control unit (MCU), field-programmable gate array (FPGA),application-specific integrated circuit (ASIC), and/or an analog controlcircuit.

Reference is now made to FIG. 6 a , which illustrates a part schematic,part block diagram of a multi-converter according to illustrativeembodiments. DC source 618 may be coupled to multi-converter 600 a.Multi-converter 600 a may be an implementation of multi-converter 300 ofFIG. 3 . Multi-converter 600 a may comprise DC-to-DC converter 619 thatmay be similar to DC-to-DC converter 302 of FIG. 3 . Terminal S3, whichmay be coupled to the output of DC-to-DC converter 619, may also be anoutput terminal of multi-converter 600 a. Multi-converter 600 a may beconfigured to output an AC voltage at terminal S1 with respect toterminal S3 and to output an AC voltage at terminal S2 with respect toterminal S3. The voltage at the second terminal of DC source 618 withrespect to the first terminal of DC source 618 may be V_(DC). DC-to-DCconverter 619 may be configured to output a DC voltage of about V_(DC)/2with respect to the first terminal of DC source 618. Multi-converter 600a may comprise block 624 a and block 624 b. Block 624 a and block 624 bmay comprise similar components. Block 624 a is described herein belowin detail. Block 624 a may comprise block 625, which may compriseswitches 614 a and/or 614 c. In some embodiments, only switch 614 a orswitch 614 c may be present.

In block 624 b, switches 611 b and 611 a are connected in series withcapacitor 610. The output of block 608 connects across the seriesconnection of switches 611 b and 611 a and capacitor 610. The seriesconnection of switches 609 a and 609 b connect across capacitor 610.Terminal S2 may be provided at the connection between switches 609 a and609 b. Block 623 may provide similar circuit connections as block 624 bwith respect to switches 605 a and 605 b wired in series with capacitor604 and switches 606 a and 606 b connected in series and acrosscapacitor 604. Terminal S1 is provided at the point where switches 606 aand 606 b are connected in series and the series connection between 605a and 605 b may be connected across the input of block 608.

Still further with respect to block 624 b, capacitor 613 may beconnected across the series connection of switches 611 a and 611 b.Capacitor 613 may be wired in series between switches 612 a and 612 bwhich are further connected across DC source 618. Switch 614 d isconnected at the point of connection between switch 612 a/capacitor 613and terminal S3. In a similar way, switch 614 b is connected at thepoint of connection between switch 612 b/capacitor 613 and terminal S3.

In some embodiments, switch 614 a may couple the first terminal ofcapacitor 602 to the output of DC-to-DC converter 619, while the secondterminal of capacitor 602 is coupled to DC source 618 through switch 603b and/or when switch 603 a is off. Similarly, switch 614 c may couplethe second terminal of capacitor 602 to the output of DC-to-DC converter619 when the first terminal of capacitor 602 is coupled to DC source 618through switch 603 a and/or when switch 603 b is off. Coupling one ofthe terminals of capacitor 602 to the output of DC-to-DC converter 619may clamp the voltage to the voltage at the output of DC-to-DC converter619. Clamping and/or voltage clamping may comprise shifting the DCvoltage at a first terminal and the voltage at a second terminal of anelectrical part having two terminals by about the same value, in a waythat the differential voltage between the first terminal and the secondterminal does not substantially change. The average voltage at thesecond terminal of capacitor 602 with respect to the first terminal ofcapacitor 602 may be about half of the voltage of DC source 618.

Still referring to FIG. 6 a , multi-converter 600 a may comprise block623. Block 623 may comprise two inputs. The first input may be coupledto the first terminal of capacitor 602, and the second input may becoupled to the second terminal of capacitor 602. The voltage at thesecond input of block 623 with respect to the first input of block 623may be referred to as the input voltage of block 623. The input voltageof block 623 may be clamped to various voltages by switching switches603 a, 603 b, 614 a and/or 614 c. The output of block 623 may be coupledto terminal S1 and may be switched between the two input voltages. Block625 and/or switches 603 a and 603 b may change the clamping point of theinput voltage of block 623. For example, the voltage at the secondterminal of DC source 618 with respect to the first terminal of DCsource 618 may be V_(DC) and the voltage at the second terminal ofcapacitor 602 with respect to the first terminal of capacitor 602 may beV_(DC)/2.

When switch 603 a is “off” and switch 614 a is “on”, the voltage at thesecond terminal of capacitor 602 with respect to the first terminal ofDC source 618 may be V_(DC) and the voltage at the first terminal ofcapacitor 602 with respect to the first terminal of DC source 618 may beV_(DC)/2. When switch 614 a is “off” and switch 603 a is “on”, thevoltage at the second terminal of capacitor 602 with respect to thefirst terminal of DC source 618 may be about V_(DC)/2 and the voltage atthe first terminal of capacitor 602 with respect to the first terminalof DC source 618 may be about zero. Similarly, to capacitor 602, theaverage voltage at the second terminal of capacitor 604 with respect tothe first terminal of capacitor 604 may be about half of the voltage atthe second terminal of capacitor 602 with respect to the first terminalof capacitor 602.

Switches 606 a and 606 b may switch in a complementary manner. Theswitching of switches 606 a and 606 b may set the output voltage atterminal S1. For example, when switch 606 a is “on” and switch 606 b is“off”, terminal S1 may be coupled to the second terminal of capacitor604, and when switch 606 a is “off” and switch 606 b is “on”, terminalS1 may be coupled to the first terminal of capacitor 604. The voltage atterminal S1 may be an AC voltage with respect to terminal S3.

Still referring to FIG. 6 a , multi-converter 600 a may comprise block608. Block 608 may provide an electrical connection between capacitors602, 604, 610 and 613, which may provide paths for current sharingbetween capacitors 602, 604, 610 and 613. Block 608 may reduce theswitching ripple across capacitors 602, 604, 610 and 613, e.g., byallowing current sharing that may result in superposition of currentripples in a manner that reduces a magnitude of associated currentripples

Reference is now made to FIG. 6 b , which illustrates a schematicdiagram of a multi-converter according to illustrative embodiments. DCsource 618 may be coupled to multi-converter 600 b. Multi-converter 600b may be similar to multi-converter 600 a of FIG. 6 a . Switches 620 a .. . 620 d, inductor 620 and capacitor 622 may be parts of resonantswitched capacitor circuit (RSCC) 626. RSCC 626 may be a possible partof a DC-to-DC converter similar to DC-to-DC converter 619 of FIG. 6 a .In RSCC 626, switch 620 a is wired in series with inductor 621,capacitor 622 and switch 620 d. The series connection of switch 620 a,inductor 621, capacitor 622 and switch 620 d may be connected across DCsource 618. Switches 620 b and 620 c are wired in series and across theseries connection of inductor 621 and capacitor 622. The point ofconnection between switches 620 b and 620 c may provide terminal S3 andconnection to the remaining portion of multi-converter 600 b at theseries connection between switches 614 a and 614 c.

The series connection between switches 614 a and 614 c may be connectedacross capacitor 602. A series connection of switch 603 b, capacitor 602and switch 603 a may be connected across DC source 618. A seriesconnection of switch 605 b capacitor 604 and switch 605 a may beconnected across capacitor 602. A series connection of switches 606 aand 606 b may be connected across capacitor 604. The connection betweenswitches 606 a and 606 b may provide terminal S1.

A series connection of switches 612 b, capacitor 613 and switch 612 amay be connected across DC source 618. A series connection of switch 611b, capacitor 610 and switch 611 a may be connected across capacitor 613.A series connection of switches 609 a and 609 b may be connected acrosscapacitor 610. The point of connection between switches 609 a and 609 bmay provide terminals S2.

Switch 608 b connects between the point where switch 611 a connects tocapacitor 613 and the point where switch 605 b connects to switch 614c/switch 603 b. Switch 608 a connects between the point where switch 611b connects to capacitor 613 and the point where switch 605 a connects toswitch 614 a/switch 603 a.

RSCC 626 may be configured to output a voltage that may be about half ofthe voltage of DC source 618. In some embodiments, instead of a part ofblocks 624 a and 624 b of FIG. 6 a , capacitors 602 and 613 and theswitches used for voltage clamping may be part of a capacitor circuitthat may be a part of RSCC 626, similar to capacitor circuit 408 of FIG.4 a.

Still referring to FIG. 6 b , switches 608 a and 608 b may be parts ofblock 627, which may be a possible part of block 608. When switch 608 ais “on”, it may provide an electrical connection between the firstterminal of capacitor 602 and the second terminal of capacitor 613. Whenswitches 605 a and 608 a are “on”, there may be an electrical connectionbetween the first terminal of capacitor 604, the first terminal ofcapacitor 602 and the second terminal of capacitor 613. When switches611 b and 608 a are “on”, there may be an electrical connection betweenthe second terminal of capacitor 610, the first terminal of capacitor602 and the second terminal of capacitor 613. When switch 608 b is “on”,it may provide an electrical connection between the first terminal ofcapacitor 613 and the second terminal of capacitor 602. When switches611 a and 608 b are “on” there may be an electrical connection betweenthe first terminal of capacitor 610, the first terminal of capacitor 613and the second terminal of capacitor 602. When switches 605 b and 608 bare “on”, there may be an electrical connection between the secondterminal of capacitor 604, the first terminal of capacitor 613 and thesecond terminal of capacitor 602. The electrical connection describedabove may provide paths for current sharing between capacitors 602, 604,610 and 613. Block 627 may reduce the switching ripple across capacitors602, 604, 610 and 613, e.g., by allowing current sharing that may resultin superposition of current ripples in a manner that reduces a magnitudeof associated current ripples.

Reference is now made to FIG. 7 , which illustrates a block diagram ofan electrical system having a multi-converter according to illustrativeembodiments. Multi-converter 702 may comprise direct-current toalternating current (DC-to-AC) converter 703 and DC-to-DC converter 704.DC-to-AC converter 703 and DC-to-DC converter 704 may be configured toreceive input power from DC source 701. DC-to-AC converter 703 may beconfigured to output a first AC voltage at output 702 a and a second ACvoltage at output 702 b. DC-to-DC converter 704 may be configured tostep down the DC voltage received from DC source 701 by about half(e.g., receive an input DC voltage of about 340V and output a voltage ofabout 170V) at output 702 c. Group of loads 705 a and group of loads 705b may be coupled to multi-converter 702 and may each comprise one ormore loads. If groups of loads 705 a and 705 b are substantiallybalanced (i.e., group of loads 705 a consumes substantially the sameamount of power as group of loads 705 b), currents flowing throughoutputs 702 a and 702 b may be substantially equal in magnitude and thevoltage at output 702 c may be about half of the voltage of DC source701 even without active voltage control (e.g., by DC-to-DC converter704). If group of loads 705 a and group of loads 705 b are notsubstantially balanced (e.g., group of loads 705 a consumes more powerthan group of loads 705 b), DC-to-DC converter 704 may regulate thevoltage at output 702 c to about half of the voltage of DC source 701 bysupplementing and/or absorbing a current difference between group ofloads 705 a and group of loads 705 b.

For example, a voltage source of 1V supplying voltage to two loadsconnected in series. If the two loads are substantially balanced (e.g.,both require 1 Watt (W) of power) then the voltage between the two loadsmay be the same, in this example it would be 0.5 Volt (V), which is halfof the voltage source. In this case, the same current may flow throughboth loads. If the first load requires 1 W and the second load requires2 W of power, and a DC-to-DC converter is balancing the voltage betweenthem (i.e., each load is supplied by 0.5V), then the currents flowingthrough each load may be different: the current flowing through thefirst load may be 2 Amps (A) and the current flowing through the secondload may be 4 A. The DC-to-DC converter may supplement and/or absorb(depending on the polarity of the voltage source and the imbalance ofthe loads) the 2A difference in current. Therefore, reducing imbalancebetween the two loads may reduce the current and/or power flowingthrough the DC-to-DC converter. Similarly, a difference in power betweengroup of loads 705 a and group of loads 505 b may result in a currentflowing through output 702 c. Reducing imbalance between group of loads705 a and group of loads 705 b may reduce the current and/or powerflowing through DC-to-DC converter 704, as was shown in the lastexample.

For example, keeping current and/or power flowing through DC-to-DCconverter 704 to a low value may allow components having a low-powerrating to be used for converter 704, which may result in cost savingswhen implementing converter 704. As an additional example, keepingcurrent and/or power flowing through DC-to-DC converter 704 to a lowvalue may increase the operational efficiency of converter 704. Asanother example, keeping current and/or power flowing through DC-to-DCconverter 704 to a low value may reduce the amount of heat that may bedissipated from DC-to-DC converter 704.

Still referring to FIG. 7 , some embodiments may include loads 706 thatmay be coupled to output 702 a and to output 702 b. Loads 706 may beconfigured to be coupled to an AC power source. For example, the voltageat output 702 a with respect to output 702 c and the voltage at output702 b with respect to output 702 c may be about 120V RMS and with abouta 180-degree phase difference with respect to each other. The voltage atoutput 702 a with respect to output 702 b may be about 240V RMS. Loads706 may be configured to be coupled to a 240V RMS power source, whichmay be provided by coupling loads 706 between outputs 702 a and 702 b.

Reference is now made to FIG. 8 a , which illustrates a block diagram ofan electrical system that includes a multi-converter according toillustrative embodiments. DC source 801 may be coupled tomulti-converter 802. Multi-converter 802 may be similar tomulti-converter 207 of FIG. 2 a . Outputs 802 a, 802 b and 802 c ofmulti-converter 802 may be coupled to switching device 806. Switchingdevice 806 may be coupled to one or more loads of loads 805 a . . . 805n. Multi-converter 802 may comprise DC-to-AC converter 803 and DC-to-DCconverter 804. DC-to-AC converter 803 may be similar to DC-to-ACconverter 202 and DC-to-DC converter 804 may be similar to DC-to-DCconverter 204 of FIG. 2 a . Switching device 806 may comprise switchesthat may couple loads of loads 805 a . . . 805 n to output 802 c and tooutput 802 a or output 802 b. Switching device 806 may change thecoupling of one or more loads of loads 805 a . . . 805 n from output 802a to output 802 b of multi-converter 802 and/or from output 802 b tooutput 802 a by changing the state of one or more switches. Loadscoupled to output 802 a may be referred to as a first group of loads,and loads coupled to output 802 b may be referred to as a second groupof loads. Switching device 806 may comprise a controller and/or may beconfigured to receive a control signal that may be configured todecrease the difference between the power and/or current associated withthe first group of loads and the power and/or current associated withthe second group of loads by changing the state of the switches ofswitching device 806. Reducing the imbalance of the two groups maydecrease the current and/or the power flowing through DC-to-DC converter804 as described above.

In some embodiments, switching device 806 may have a user interface,e.g., a panel with a monitor and buttons or a GUI displayed on a monitorcoupled to input devices such as a keyboard, a mouse and/or atouchscreen. The user interface may provide information regarding loadsof loads 805 a . . . 805 n that may be coupled to switching device 806,information regarding the state of the switches (such as which loads maybe coupled to which output terminals of DC-to-AC converter 803, how muchpower or current may be associated with a load and/or a group of loads)and/or information regarding the power and/or current flowing throughDC-to-DC converter 804. The user interface may receive one or moreconstraints from a user such as forcing a load to couple to a certainoutput terminal of DC-to-AC convert 803.

In some embodiments, switching device 806 and/or a controller configuredto control switching device 806 may comprise a communication deviceenabling communication with one or more devices such as an access pointor a smartphone with a connection to the internet. In some embodiments,which may include a user interface, a connection to the internet may beused to display a GUI in a web browser or an application on a monitor.In some embodiments, switching device 806 may be configured to receiveone or more signals from a remote control (e.g., a user controllingwhich loads are connected to which output via a smartphone or a remotecontrol with an infra-red (IR) transmitter or transceiver).

Still referring to FIG. 8 a , some embodiments may include loads 807that may be similar to loads 706 of FIG. 7 . Loads 807 may be coupled tooutput 802 a and output 802 b.

Reference is now made to FIG. 8 b , which illustrates a block diagram ofa switching system according to illustrative embodiments. Switchingdevice 812 may be an implementation of switching device 806 of FIG. 8 a. Loads 814 a . . . 814 n may be similar to loads 805 a . . . 805 n ofFIG. 8 a . Switching device 812 may couple one or more loads of loads814 a . . . 814 n to input 815 c and to input 815 a or input 815 b.Switching device 812 may comprise switches 813 a . . . 813 n. Eachswitch of switches 813 a . . . 813 n may link a load of loads 814 a . .. 814 n to two of the inputs as described above. For example, each loadmay have a first terminal and a second terminal, each switch of switches813 a . . . 813 n may comprise a third terminal, a fourth terminal and acommon terminal. Each load may be coupled to a switch. The firstterminal of a load may be coupled to a common terminal of a switch. Thesecond terminal of a load may be coupled to input 815 c. The thirdterminal of a switch may be coupled to input 815 a and the fourthterminal may be coupled to input 815 b. A switch of switches 813 a . . .813 n may comprise a first state and a second state. The first state ofa switch may couple the common terminal to the third terminal, and thesecond state of a switch may couple the common terminal to the fourthterminal. According to the above coupling of the illustrated elements,changing the state of a switch may allow to change the coupling of aload from input 815 a to 815 b and vice versa, i.e., switching a loadfrom the first group of loads to the second group of loads.

Switch 813 a and 813 b of FIG. 8 b are illustrated using single polemultiple throw switches. In some embodiments, a plurality ofsingle-pole-single-throw switches may be used. For example, a pair oftransistors (e.g. MOSFETs) may be used to implement switch 813 a, afirst transistor disposed between load 814 a and input 815 a and asecond transistor disposed between load 814 a and input 815 b, witheither the first transistor or the second transistor in the “on”position when power is provided to load 814 a.

In some embodiments, where the input power is oscillating in asinusoidal manner, the moment when a switch of switches 813 a . . . 813n is switched may affect one or more loads of loads 814 a . . . 814 n.For example, for some loads (e.g., capacitive loads) it may bepreferable to switch when the AC voltages are at zero (e.g., when S5 andS6 of FIG. 2 b are at zero) and for some loads (e.g., inductive loads)it may be preferable to switch when the AC currents are at zero.

If a switch of switches 813 a is switched when the voltage is at itspeak value (e.g., when S4 of FIG. 2 b is at V_(DC)), then there may be afast change in the voltage, capacitive loads may be affected.

Still referring to FIG. 8 b , control signal 816 may be configured tocontrol the state of the switches. Control signal 816 may be provided byan external device (e.g., a controller configured to controlmulti-converter 802) and/or a controller that may be a part of switchingdevice 812.

In some embodiments, switching device 812 may measure and/or sense oneor more electrical parameters (e.g., the current and/or power)associated with each load or group of loads of loads 814 a . . . 814 n,and may send one or more of the measurements to a controller.Communication with a controller may be implemented in various methodssuch as power line communication (PLC), wired communication, wirelesscommunication, acoustic communication, etc.

In some embodiments a controller configured to control the switches ofswitching device 812 may be configured to receive measurement ofelectrical parameters (e.g., voltage, current and/or power) associatedwith loads from a smart house system such as smart outlets or smartloads that may be able to communicate with the controller.

Reference is now made to FIG. 8 c , which illustrates a block diagram ofa switching system according to illustrative embodiments. Switches 823 a. . . 823 n may be similar to switches 813 a . . . 813 n. Switches 813 a. . . 813 n may be a part of a single switching device, whereas switches823 a . . . 823 n may each be a part of a smart outlet of smart outlets822 a . . . 822 n. Smart outlets 822 a . . . 822 n may switch loads frominput 825 a to input 825 b and/or from input 825 b to input 825 a. Asmart outlet of smart outlets 822 a . . . 822 n may measure and/or sensecurrent and/or power associated with a load of loads 824 a . . . 824 nthat may be coupled to the smart outlet. Smart outlets 822 a . . . 822 nmay be configured to receive control signal 826. Smart outlets 822 a . .. 822 n may communicate with a controller and may send electrical (e.g.,current power and/or voltage) measurements associated with loads 824 a .. . 824 n.

Communication with a controller may be implemented in various methodssuch as power line communication (PLC), wired communication, wirelesscommunication, acoustic communication, etc. For example, each load ofloads 824 a . . . 824 n may have a first terminal and a second terminal.Each smart outlet of smart outlets 822 a . . . 822 n may comprise aswitch of switches 823 a . . . 823 n. Each switch of switches 823 a . .. 823 n may comprise a third terminal, a fourth terminal and a commonterminal. Each load may be coupled to a switch of switches 823 a . . .823 n. The first terminal of a load may be coupled to a common terminalof a switch. The second terminal of a load may be coupled to input 825c. The third terminal of a switch may be coupled to input 825 a and thefourth terminal may be coupled to input 825 b. A switch of switches 823a . . . 823 n may comprise a first state and a second state. The firststate of a switch may couple the common terminal to the third terminal,and the second state of a switch may couple the common terminal to thefourth terminal. According to the above coupling of the illustratedelements, changing the state of a switch may allow to change thecoupling of a load from input 825 a to 825 b and vice versa. Smartoutlets 822 a . . . 822 n may control the state of switches 823 a . . .823 n according to control signal 826.

Reference is now made to FIG. 8 d , which illustrates a graphical userinterface (GUI) application of a switching device. The application maybe configured to control a switching device such as switching device 806of FIG. 8 a , switching device 812 of FIG. 8 b and/or smart outlets 822a . . . 822 n of FIG. 8 c . The application may provide a control signal(such as control signal 816 of FIG. 8 b and/or control signal 826 ofFIG. 8 c ) to a switching device. The application may provide a list ofloads 833 (e.g., loads 805 a . . . 805 n of FIG. 8 a , loads 814 a . . .814 n of FIG. 8 b , and/or loads 824 a . . . 824 n of FIG. 8 c ). Theapplication may provide a descriptive name of each load (e.g. “diningroom outlet #1”, “Master bedroom lights”). In some embodiments, whereindividual load values are available, the application may provide thecurrent load value for each load. In some embodiments, the applicationmay indicate the group of loads currently associated with each load onthe list. The application may provide an option for manually changingthe group of loads associated with a load. For example, a user mayactivate (e.g., using a touchscreen on a mobile phone, or a mouse on acomputer) button 834 to change the mode from automatic to manual andvice versa. When in Automatic Mode, a program may be enabled, theprogram configured to set the association of one or more loads with agroup of loads. For example, when in automatic mode, a controller isconfigured to operate switching device 806 to connect each load to afirst group of loads or to a second group of loads. When in Manual Mode,the program may be disabled and/or may allow a user to set theassociation of one or more loads to a group of loads. In anotherexample, a user may activate one or more of the “Switch Group” buttons831, and be presented with the option of switching a load from a firstgroup of loads to a second group of loads. Such an action may bedesirable when a system maintainer (e.g., installer or electricalworker) would like to shut down a part of the electrical system (e.g.,routine maintenance of the electrical system) and would like to firstchange the association of one or more loads with a group of loadsconnected to that part of the electrical system to a different group ofloads that is connected to a different part of the electrical system. Insome embodiments, automatic division of loads amongst different groupsof loads may result in suboptimal division (e.g., with one group ofloads consuming substantially more power than a second group of loads),and manual corrections may be beneficial.

Still referring to FIG. 8 d , the application may be connected to wiredcommunication networks, wireless communication networks, and/or datanetwork(s), including an intranet or the Internet. The application mayreceive data from and send commands to system devices (e.g.,multi-converter 802, loads 805 a . . . 805 n and/or switching device 806of FIG. 8 a ) via a computing device on which the application isexecuting. In addition to providing information and control-relatedservices to the end user, the application may receive notification of apotentially unsafe condition from one or more system-connected controland/or communication devices, and warn the user (e.g., a user and/or asystem maintenance worker). These warnings may be audio and/or visual.They may, for example, be a pop-up window, text message, beep, tone,siren, LED, and/or high lumen LED. For example, when the current and/orpower flowing through input 815 c of FIG. 8 b is above a predeterminedthreshold, the application may display in textbox 832 a warning message.The warning message may be triggered by the application or by acontroller and/or communication device included in the switching device,such as switching device 806 of FIG. 8 a and/or switching device 812 ofFIG. 8 b ) and/or included in a multi-converter (such as multi-converter802).

It is to be understood that the application as illustrated in FIG. 8 dis merely an illustrative embodiment. User-interface applications mayoffer many additional features such as time and date indications,graphical system illustrations, communication services, weatherforecasts, generation and load forecasts, service call capabilities andmore. Furthermore, some applications may serve several electrical powersystems, with a user able to scroll between screens indicating differentelectrical systems, and view and control each system individually.

Reference is now made to FIG. 9 , which illustrates a block diagram of athree-phase multi-converter according to illustrative embodiments. DCsource 901 may be coupled to three-phase multi-converter 902.Three-phase multi-converter 902 may comprise outputs 903 a . . . 903 d.Outputs 903 a-903 c may provide AC voltages with respect to output 903 dwith about the same voltage amplitude and/or RMS value and about thesame frequency and about ±120 degrees phase shift with respect to eachother. Output 903 d may provide a DC voltage of about half of the inputDC voltage.

Still referring to FIG. 9 , the voltage between output 903 a and 903 bmay be Vab, the voltage between output 903 b and 903 c may be Vbc andthe voltage between output 903 c and 903 a may be Vca. In someembodiments, voltages Vac, Vbc and Vca may be AC voltages with about thesame voltage amplitude and/or RMS value and about the same frequency andabout ±120 degrees phase shift with respect to each other. The voltagebetween output 903 a and output 903 d may be Vad and the voltage betweenoutput 903 d and output 903 b may be Vdb. In some embodiments, Vad maybe equal to Vdb, and Vcd may have a voltage amplitude and/or RMS valueof about √3 of the voltage amplitude and/or RMS value of Vad, and have aphase shift of about π/2 with respect to Vad and Vbd. For example, Vadmay be 170 sin(wt) (120V RMS), Vbd may be 170 sin(wt+π) (120V RMS) andVcd may be 294 sin(wt+π/2) (208V RMS).

Reference is now made to FIG. 10 , which illustrates a block diagram ofa three-phase multi-converter according to illustrative embodiments.Three-phase multi-converter 1000 may be similar to three-phasemulti-converter 902 of FIG. 9 . DC source 1001 may be coupled tomulti-converter 1000. Multi-converter 1000 may comprise DC-to-DCconverter 1002 and three-phase DC-to-AC converter 1003. DC-to-DCconverter 1002 may be similar to DC-to-DC converter 302 of FIG. 3 . Insome embodiments, DC-to-DC converter 1002 may include a resonantswitched capacitor circuit. Output 1004, 1005 and 1006 may provide ACvoltages with about the same voltage amplitude and/or RMS value andabout the same frequency and with a phase shift of ±120 degrees withrespect to the other two outputs. For example, the voltage at the secondterminal of DC source 1001 may be V_(DC) with respect to the firstterminal of DC source 1001. DC source 1001 connects to inputs 1008 a and1800 b of multi-converter 1000. The voltage at outputs 1004, 1005 and1006 may be 0.5(V_(DC)+V_(DC)*sin(2πft)),0.5(V_(DC)+V_(DC)*sin(2πft+2π/3)), 0.5(V_(DC)+V_(DC) sin(2πft+4π/3))respectively in reference to the first terminal of DC source 1001. Thevoltage at output 1007 may be a DC voltage of about half of the voltageof DC source 1001 with respect to the first terminal of DC source 1001.

Reference is now made to FIG. 11 a , which illustrates a circuittopology of a converter 1100A according to illustrative embodiments.Converter 1100A may be described as a circuit for inverting a resonantswitched capacitor with unity gain. An input voltage V_(in) may beapplied across terminals V_(in) and G. Connected across terminals V_(in)and G may be capacitor C_(in). An output voltage V_(out) may be derivedacross terminals V_(out) and G, described in greater detail below as aresult of converter 1100A converting the input voltage V_(in) onterminals V_(in) and G to an output voltage V_(out) on terminals V_(out)and G. Output capacitor C_(out) connects across terminals V_(out) and G.A load (not shown) may be connected across terminals V_(out) and G. Theload may be a DC-to-AC converter such as DC-to-AC converters 202, 204,303, 410, 703, 704, 803 and 1003 described above. Converter 1100A andother converters described below is a similar to resonant switchedcapacitor circuit 414 described above.

Terminal G may or may not be connected to ground and/or earth dependingon the desired operating functions of the converters. By way ofnon-limiting example of a desired operating function, input voltageV_(in) on terminals V_(in) and G may not have terminal G connected toground and/or earth in order that input voltage V_(in) and/or outputvoltage V_(out) may be floating voltages.

With respect to the discussions that follow, terminal G may be assumedto be connected to ground and/or earth. In general converters describedin greater detail below may be with respect to the topologies that canbe extended to give step-down converters with conversion ratios of onehalf and/or one third, step-up converters with conversion ratios twoand/or three, and inverting converters with conversion ratios of a halfand/or a third. Descriptions that follow mainly refer to converters thatconvert a direct current (DC) input voltage (V_(in)) to a DC outputvoltage (V_(out)). As such by way of non-limiting example with referenceto FIG. 11 a , the term “inverting” converter means that voltageV_(out)=−V_(in), in other words the output voltage (V_(out)) is theinverse of the input voltage (V_(in)).

Switches S_(W1), S_(W2), S_(W1a) and S_(W2a) are connected in series.The series connection of switches S_(W1), S_(W2), S_(W1a) and S_(W2a)are connected in parallel across terminals V_(in) and V_(out). The pointat which switch S_(W2) connects to switch S_(W1a) also connects toterminal G. A series connection of inductor L_(r) and capacitor C_(r)connects across switches S_(W2) and S_(W1a) respectively where switchS_(W1) connects to switch S_(W2) and switch S_(W1a) connects to switchS_(W2a).

Each of the switches S_(W1), S_(W2), S_(W1a) and S_(W2a) may have a bodydiode connected across each switch and/or the body diode of each switchmay be an integral part of a switch. Switches S_(W1), S_(W2), S_(W1a)and S_(W2a) and other switches discussed above as well as below indescription that follow may be semiconductor switches such as metaloxide semiconductor field effect transistors (MOSFETs), insulated gateFETs (IGFETs), insulated gate bipolar junction transistors (IGBJTs)and/or junction FETs (JFETs). Switches S_(W1), S_(W2), S_(W1a) andS_(W2a) and may be mechanical and/or electro-mechanical switches such assingle pole double throw switches and/or relays.

Reference is now made to FIG. 11 b , which illustrates a circuittopology of a converter 1100B according to illustrative embodiments.Converter 1100B is similar to converter 1100A in that both are unitymode inverting converters where V_(out)=−V_(in), in other words theoutput voltage (V_(out)) is the inverse of the input voltage (V_(in)).Converter 1100B is similar to converter 1100A except that now capacitorC_(r) is connected across switches S_(W2) and S_(W1a) respectively whereswitch S_(W1) connects to switch S_(W2) and switch S_(W1a) connects toswitch S_(W2a). Inductor L_(r) now connects between the point whereswitch S_(W2) connect to switch S_(W1a) and terminal G. A (load notshown) may be connected across terminals V_(out) and G. Converter 1100Bmay be described as a unity mode, resonant switched-capacitor converterwith modified inductor position.

Reference is now made to FIG. 11 c , which show three graphs of voltageversus time according to illustrative embodiments. Operation ofconverters 1100A and 1100B may be such that when S_(W1) and S_(W1a) areturned “on”, in a first interval (T_(res)), inductor L_(r) and capacitorC_(r) resonate and current I_(Lr) starts to vary sinusoidally. In thegraph (a), switch S_(W1a) (shown by dotted line) is turned “off” beforehalf the resonant period and the body diode of S_(W1a) starts to conductcurrent I_(Lr) and the resonance stops when current I_(Lr) reaches zero.Switch S_(w1) is turned “off” (shown with solid line) with zero currentafter switch S_(W1a) (shown by dotted line) is turned “off”. During thefirst interval (T_(res)), energy is transferred from the input voltageV_(in) to capacitor C_(r).

In the graph (b), in the second interval (T_(sw)-T_(res)), the switchesS_(w2) and S_(w2a) are turned “on” with zero current. The inductor L_(r)and capacitor C_(r) start to resonate and the energy in the capacitorC_(r) is transferred to the output terminals V_(out). Similar to theprevious interval, the switch S_(W2a) (shown by dotted line) is turned“off” before half the resonant period to achieve zero current turn “off”for the switch S_(W2) that is turned “off” after switch S_(W2a) (shownby dotted line) is turned “off”. For the circuit topologies ofconverters 1100A and 1100B, turn-“on” of all the switches and turn-“off”of switches S_(W1) and S_(W2) occurs at zero-current.

Graph (c) shows for both converters 1100A and 1100B, three plots of theinput voltage V_(in) (shown by closer dotted line), the output voltageV_(out) and the voltage across capacitor C_(r). Graph (c) shows that theoutput voltage (V_(out)) is the inverse of the input voltage (V_(in))with unity gain.

Reference is now made to FIG. 11 d , which shows two graphs 1102A and1102B according to illustrative embodiments. FIG. 11 d shows adifference between converters 1100A and 1100B. The difference betweenconverters 1100A and 1100B may be in respect to inductor current I_(Lr).Graphs 1102A and 1102B show a plot of resonant inductor current I_(Lr)versus time respectively for converter 1100A and 1100B. From graph 1102Bit can be seen that converter 1100B has lower inductor (I_(Lr)) ripplecurrent compared to graph 1102A for converter 1100A. As such animplementation of converter 1100B compared to an implementation ofconverter 1100A may result in a lower inductor volume for inductorL_(r).

For converter 1100A, graph 1102A, inductor current I_(Lr) resonates in apositive direction in interval one (T_(res)) and resonates in negativedirection in interval two (T_(sw)-T_(res)) and the ripple in inductorcurrent is 2×I. However, for converter 1100B the inductor current I_(Lr)is always in the same direction and hence a reduced magnitude of ripplecurrent of 1×I.

Reference is now made to FIG. 11 e , which illustrates a circuittopology of a converter 1100C according to illustrative embodiments.Converter 1100C is a three-leg inverting unity mode resonant switchedcapacitor converter that includes three inverting resonant switchedcapacitor converters operating 120 degrees out of phase relative to eachother. Leg1 that is similar to Leg2 and Leg3 includes a seriesconnection of switches S₁₁, S₂₁, S_(1a1) and S_(2a1) that is connectedacross terminals V_(in) and V_(out). In general, the end subscriptnumeral “1” of Leg1 includes switches S₁₁, S₂₁, S_(1a1) and S_(2a1),capacitor C_(r1) and inductor L_(r1). The end numerical subscripts “2”and “3” respectively correspond capacitors (C_(r2) and C_(r3)) andinductors (L_(r2) and L_(r3)) in respective Leg2 and Leg3. As such Leg2includes switches S₁₂, S₂₂, S_(1a2) and S_(2a2), capacitor C_(r2), andinductor L_(r1). Leg3 includes switches S₁₃, S₂₃, S_(1a3) and S_(2a3),capacitor C_(r3), and inductor L_(r1). Each switch in each of Leg1, Leg2and Leg3 may have its own body diode connected across each switch. Aload (not shown) may be connected across terminals V_(out) and G.

Using Leg1 that adequately explains the connections of the other legs,capacitor C_(r1) connects across switches S₂₁ and S_(1a1) at the pointswhere S₂₁ connects to switch S₁₁ and switch S_(1a1) connects to switchS_(2a1). Inductor L_(r1) of Leg1 connects to terminal G and to the pointwhere switch S₂₁ connects to switch S_(1a1). Capacitor C_(in) connectsacross terminals V_(in) and G. Capacitor C_(out) connects acrossterminals G and V_(out).

In operation, each leg of converter 1100C handles one third of the powerconverted from input to output of converter 1100C. The ripple currenthandled by the input capacitor C_(in) and output capacitor C_(out) isthe sum of the currents through three currents I_(r1), I_(r2) and I_(r3)that are 120 degrees out of phase to each other as such the use of threelegs may reduce ripple current rating of capacitors C_(in), and C_(out).In sum, converter 1100C may provide lower inductor ripple current byvirtue of relocating inductors that may result in inductors with lowerinductor volume and utilization of one or more legs that may lowerripple current ratings for capacitors C_(in) and C_(out).

In general, for the descriptions that follow, reference is made totopologies that can be extended to step-down, step-up, and invertingconverters with various conversion ratios. More specifically, thetopologies can be extended to step-down converters with conversionratios of one half and/or one third, step-up converters with conversionratios two and/or three, and inverting converters with conversion ratiosof a half and/or a third.

The figures and their descriptions that follow show similar converters.For example, a difference between a converter similar to anotherconverter may be that one converter of a first type may utilize theseries connection of inductor L_(r) and capacitor C_(r) connected acrossto serially connected switches (S_(W2) and S_(w1a) for example) in theconverter topology. Whereas another converter of a second type may havecapacitor C_(r) connected across serially connected switches (S_(W2) andS_(w1a) for example) and inductor L_(r) located and/or connected betweenthe serial connected switches (switches S_(W2) and S_(w1a)) andcapacitors C_(in) and/or C_(out).

In general, for topologies described below for converters of the firstand/or second type, multi-legged versions of converters similar to FIG.11 d may be realized. A benefit of multi-legged versions for convertersof the first and/or second type may provide lower ripple current ratingsfor capacitors C_(in) and/or C_(out). In particular for the convertersof the second type when compared to the first type, a lower inductorripple current may be provided by virtue of the relocation of inductorsas shown previously in FIGS. 11 b and 11 e . Consequently,implementation of the type two converter may see an inductor L_(r) thatmay be implemented with a lower inductor volume comparted to an inductorvolume for the second type of converter for when both types operateunder the same conditions. The lower inductor ripple current of thesecond converter types (converters 1100B and/or 1100C for example) maybe by virtue of the inductor current (I_(Lr)) being in the samedirection. Whereas converters of the first type may have a larger ripplecurrent due to inductor current I_(Lr) that resonates in a positivedirection in a first-time interval and resonates in negative directionin a second-time interval as described above with respect to FIG. 11 d.

Reference is now made to FIGS. 12 a and 12 b , which show respectivestep-down DC buck converters 1200A and 1200B with conversion ratios of ahalf, according to illustrative embodiments. Common to both FIGS. 12 aand 12 b is a series connection of switches S_(W1), S_(W2), S_(W1a) andS_(W2a) where each switch may have a body diode connected across theswitch and/or the body diode of each switch may be an integral part ofeach switch. Capacitor C_(in) connects between terminal V_(in) andground and/or earth. Capacitor C_(out) connects between terminal V_(out)and ground and/or earth. Terminal V_(out) connects to switch S_(W1) andground and/or earth connects to switch S_(W2a). A (load not shown) maybe connected across terminals V_(out) and ground and/or earth.

Specifically, with respect to FIG. 12 a , inductor L_(r) connects inseries with capacitor Cr and the series connection of inductor L_(r) andcapacitor C_(r) connects across the series connection of switches S_(W2)and S_(W1a). The point of connection between switches S_(W2) and S_(W1a)connects to terminal V_(out).

Specifically, with respect to FIG. 12 b , capacitor C_(r) connectsacross the series connection of switches S_(W2) and S_(W1a). InductorL_(r) connects between the point of connection between switches S_(W2)and S_(W1a) and terminal V_(out).

Reference is now made to FIG. 12 c , which show four graphs (a), (b),(c) and (d) of voltages and current versus time according toillustrative embodiments. The four graphs (a), (b), (c) and (d) are forstep-down (buck) converter 1200B with conversion ratio of a half. WhenS_(W1) and S_(W1a) are turned “on” in a first interval, inductor L_(r)and capacitor C_(r) resonate and the current I_(Lr) starts varyingsinusoidally and energy is transferred to resonant capacitor C_(r)during the first interval (T_(res)). In graph (a), switch S_(W1a) (shownby dotted line) is turned “off” before half the resonant period afterwhich switch S_(W1) (shown by solid line) is turned “off”. The diodeconnected in parallel to switch S_(W1a) starts conducting the inductorcurrent I_(Lr) and the resonance stops when the inductor current I_(Lr)reaches zero. The resonant capacitor voltage has a dc component equal to

$\frac{V_{in}}{2}$

and a small ac component. In the second interval (T_(sw)-T_(res)), shownin the second graph (b), the switches S_(W2) and S_(W2a) are turned “on”with zero current. The inductor L_(r) and capacitor C_(r) are connectedto the output terminal V_(out). Inductor L_(r) and capacitor C_(r) startresonating and the energy in capacitor C_(r) is transferred to theoutput terminal V_(out). Similar to the previous interval, the switchS_(W2a) (shown by dotted line) is turned “off” before half the resonantperiod and diode connected in parallel across switch S_(W2a) startsconducting.

In graph (c), lower inductor ripple current (I_(Lr)) converter 1200B maybe by virtue of the inductor current (I_(Lr)) being in the samedirection compared to what may be a larger bi-directional inductorripple current (I_(Lr)) of converter 1200A for example. Inductor ripplecurrent (I_(Lr)) of converter 1200B is positive.

Graph (d) shows for converter 1200B, three plots of the input voltageV_(in) (shown by wider spaced dotted line), the output voltage V_(out)(shown by narrower spaced dotted line) and the voltage across capacitorC_(r) (shown as solid line). The fourth graph (d) shows the buckoperation of converter 1200B such that the output voltage (V_(out)) islower than the input voltage (V_(in)) by virtue of a conversion ratio ofa half.

Reference is now made to FIGS. 13 a and 13 b , which show respectivestep-up DC boost converters 1300A and 1300B with conversion ratios oftwo, according to illustrative embodiments. Common to both FIGS. 13 aand 13 b is a series connection of switches S_(W1), S_(W2), S_(W1a) andS_(W2a). Capacitor C_(in) connects between terminal V_(in) and groundand/or earth. Capacitor C_(out) connects between terminal V_(out) andground and/or earth. Terminal V_(in) connects to switch S_(W1) andground and/or earth connects to switch S_(W2a).

Specifically, with respect to FIG. 13 a , inductor L_(r) connects inseries with capacitor Cr and the series connection of inductor L_(r) andcapacitor C_(r) connects across the series connection of switches S_(W2)and S_(W1a). The point of connection between switches S_(W2) and S_(W1a)connects to terminal V_(in).

Specifically, with respect to FIG. 13 b , capacitor C_(r) connectsacross the series connection of switches S_(W2) and S_(W1a). InductorL_(r) connects between the point of connection between switches S_(W2)and S_(W1a) and terminal V_(in). A comparison of the circuit topology ofFIG. 12 a with FIG. 13 a shows that the step-up converter topology ofFIG. 13 a is achieved by swapping the input and output voltageconnections of FIG. 12 a . Similarly, a comparison of the circuittopology of FIG. 12 b with FIG. 13 b shows that the step-up convertertopology of FIG. 13 b is achieved by swapping the input and outputvoltage connections of FIG. 12 b.

Reference is now made to FIG. 13 c , which shows four graphs (a), (b),(c) and (d) of voltages and current versus time according toillustrative embodiments. The four graphs (a), (b), (c) and (d) are forstep-up (boost) converter 1300B with conversion ratio of two. In graph(b), in a first interval of T_(res), S_(W2) and S_(W2a) are turned “on”,input voltage V_(in) is connected in series with inductor L_(r),capacitor C_(r). Inductor L_(r) and capacitor C_(r) resonate and theinductor current I_(Lr) starts varying sinusoidally and energy istransferred to resonant capacitor C_(r). Switch S_(W2a) (shown by dottedline) is turned “off” before half the resonant period (T_(res)) afterwhich switch S_(W2a) (shown by solid line) is turned “off”. The diodeconnected in parallel across switch S_(W2) starts to conduct inductorcurrent I_(Lr). The resonance stops when the inductor current I_(Lr)reaches zero. Resonant capacitor C_(r) voltage has a DC component equalto V_(in) and a small AC component. In the second interval(T_(SW)-T_(res)) shown in graph (a), the switches S_(W1) and S_(W1a) areturned “on” with zero current. Inductor L_(r) and capacitor C_(r) startresonating and the energy is transferred to the output terminal V_(out).Similar to previous interval the switch S_(W1) is turned “off” beforehalf the resonant period and diode connected in parallel across switchS_(W1) starts conducting.

In graph (c), lower inductor ripple current (I_(Lr)) converter 1300B maybe by virtue of the inductor current (I_(Lr)) being in the samedirection compared to what may be a larger bi-directional inductorripple current (I_(Lr)) of converter 1300A for example. Inductor ripplecurrent (I_(Lr)) of converter 1300B is negative below zero volts.

Graph (d) shows for converter 1300B, three plots of the input voltageV_(in) (shown by wider spaced dotted line), the output voltage V_(out)(shown by narrower spaced dotted line) and the voltage across capacitorC_(r) (shown as solid line). The fourth graph (d) shows the boostoperation of converter 1300B such that the output voltage (V_(out)) ishigher than the input voltage (V_(in)) by virtue of a conversion ratioof two.

Reference is now made to FIGS. 14 a and 14 b , which show respectiveinverting converters 1400A and 1400B with conversion ratios of a half,according to illustrative embodiments. Common to both FIGS. 14 a and 14b is a series connection of switches S_(W1), S_(W2), S_(W1a) andS_(W2a). Capacitor C_(in) connects between terminal V_(in) and terminalG. Capacitor C_(out) connects between terminal V_(out) and terminal G.Terminal V_(in) connects to switch S_(W1) and terminals V_(out) connectsto switch S_(W2a).

Specifically, with respect to FIG. 14 a , the point where switch S_(W2)is connected to switch S_(W1a) is also connected to terminal G. One endof inductor L_(r) connects to the point where switch S_(W1) is connectedto switch S_(W2). The other end of inductor L_(r) connects to one endoff switch S_(2b) and one end of capacitor C_(ra). The other end ofcapacitor C_(ra) connects to one end of switch S_(1b) and one end ofswitch S_(2c). The other end of switch S_(2b) connects to the other endof switch S_(1b) and one end of capacitor C_(rb). The other end ofcapacitor C_(rb) connects to the point where switch S_(W1a) connects toswitch S_(W2a). The other end of switch S_(2c) connects to terminalV_(out).

Specifically, with respect to FIG. 14 b , inductor L_(r) is connectedbetween the point where switch S_(W2) is connected to switch S_(W1a) andterminal G. The point where switch S_(W1) is connected to switch S_(W2)connects to one end off switch S_(2b) and one end of capacitor C_(ra).The other end of capacitor C_(ra) connects to one end of switch Sib andone end of switch S2 c. The other end of switch S_(2b) connects to theother end of switch Sib and one end of capacitor C_(rb). The other endof capacitor C_(rb) connects to the point where switch S_(W1a) connectsto switch S_(W2a). The other end of switch S_(2c) connects to terminalV_(out).

Reference is now made to FIG. 14 c , which shows four graphs (a), (b),(c) and (d) of voltages and current versus time according toillustrative embodiments. The four graphs (a), (b), (c) and (d) are forstep-down (buck) converter 1400B with conversion ratio of a half.

When S_(W1), S_(W1a) and S_(1b) are turned “on” in a first interval,inductor L_(r) and capacitors C_(ra) and C_(rb) connected in series byswitch Sib resonate. Current I_(L), starts varying sinusoidally andenergy is transferred to resonant capacitors C_(ra) and C_(rb) duringthe first interval (T_(res)). In graph (a), switch S_(W1a) and S_(W1b)(shown by dotted line) is turned “off” before half the resonant periodafter which switch S_(W1) (shown by solid line) is turned “off”. Thediode connected in parallel to switch S_(W1a) starts conducting theinductor current I_(Lr) and the resonance stops when the inductorcurrent I_(Lr) reaches zero. The resonant capacitor voltage has a dccomponent equal to

$\frac{V_{in}}{2}$

a small ac component. In the second interval (T_(sw)-T_(res)), shown inthe second graph (b), the switches S_(W2), S_(W2a), S_(2b) and S_(2c)are turned “on” with zero current. The inductor L_(r) and capacitorC_(rb) are connected to the output terminal V_(out). Inductor L_(r) andcapacitor C_(rb) start resonating and the energy in capacitor C_(rb) istransferred to the output terminal V_(out). Similar to previousinterval, the switch S_(W2a) (shown by dotted line) is turned “off”before half the resonant period and diode connected in parallel acrossswitch S_(W2a) starts conducting.

In graph (c), lower inductor ripple current (I_(Lr)) converter 1400B maybe by virtue of the inductor current (I_(Lr)) being in the samedirection compared to what may be a larger bi-directional inductorripple current (I_(Lr)) of converter 1400A for example. Inductor ripplecurrent (I_(Lr)) of converter 1400B is positive.

Graph (d) shows for converter 1400B, three plots of the input voltageV_(in) (shown by wider spaced dotted line), the output voltage V_(out)(shown by narrower spaced dotted line) and the voltage across capacitorsC_(ra) and C_(rb) (shown as solid line). Graph (d) shows the buckoperation of converter 1400B such that the output voltage (V_(out)) islower and negative and/or inverted compared the input voltage (V_(in))by virtue of a conversion ratio of a half.

Reference is now made to FIGS. 15 a and 15 b , which show respectivestep-down converters 1500A and 1500B with conversion ratios of a third,according to illustrative embodiments. Common to both FIGS. 15 a and 15b is a series connection of switches S_(W1), S_(W2), S_(W1a) andS_(W2a). Capacitor C_(in) connects between terminal V_(in) and groundand/or earth. Capacitor C_(out) connects between terminal V_(out) andground and/or earth. Terminal V_(in) connects to switch S_(W1) andground and/or earth connects to switch S_(W2a).

Specifically, with respect to FIG. 15 a , the point where switch S_(W2)is connected to switch S_(W1a) is also connected to terminal V_(out).One end of inductor L_(r) connects to the point where switch S_(W1) isconnected to switch S_(W2). The other end of inductor L_(r) connects toone end off switch S_(2b) and one end of capacitor C_(ra). The other endof capacitor C_(ra) connects to one end of switch Sib and one end ofswitch S2 c. The other end of switch S_(2b) connects to the other end ofswitch Sib and one end of capacitor C_(rb). The other end of capacitorC_(rb) connects to the point where switch S_(W1a) connects to switchS_(W2a). The other end of switch S2 c connects to and/or earth.

Specifically, with respect to FIG. 15 b , inductor L_(r) is connectedbetween the point where switch S_(W2) is connected to switch S_(W1a) andterminal V_(out). The point where switch S_(W1) is connected to switchS_(W2) connects to one end off switch S_(2b) and one end of capacitorC_(ra). The other end of capacitor C_(ra) connects to one end of switchS_(1b) and one end of switch S_(2c). The other end of switch S_(2b)connects to the other end of switch S_(1b) and one end of capacitorC_(rb). The other end of capacitor C_(rb) connects to the point whereswitch S_(W1a) connects to switch S_(W2a). The other end of switchS_(2c) connects to and/or earth.

A comparison of the circuit topology of FIG. 14 a with FIG. 15 a showsthe difference in connections of capacitors C_(in) and C_(out) toterminals V_(in) and V_(out) and to terminal G in FIG. 14 a andconnections of capacitors C_(in) and C_(out) to V_(in) and V_(out) andto ground and/or earth of FIG. 15 a . Similarly, with respect to FIGS.14 b and 15 b is the difference in connections of capacitors C_(in) andC_(out) to terminals V_(in) and V_(out) and to terminal G in FIG. 14 band connections of capacitors C_(in) and C_(out) to V_(in) and V_(out)and to ground and/or earth of FIG. 15 b.

Reference is now made to FIG. 15 c , which shows four graphs (a), (b),(c) and (d) of voltages and current versus time according toillustrative embodiments. The four graphs (a), (b), (c) and (d) are forstep-down (buck) converter 1500B with conversion ratio of a third. WhenS_(W1), S_(W1a) and S_(1b) are turned “on” in a first interval, inductorL_(r) and capacitors C_(ra) and C_(rb) connected in series by switchS_(1b) resonate. Current I_(Lr) starts varying sinusoidally and energyis transferred to resonant capacitors C_(ra) and C_(rb) during the firstinterval (T_(res)). In graph (a), switch S_(W1a) and S_(W1b) (shown bydotted line) is turned “off” before half the resonant period after whichswitch S_(W1) (shown by solid line) is turned “off”. The diode connectedin parallel to switch S_(W1a) starts conducting the inductor currentI_(Lr) and the resonance stops when the inductor current I_(Lr) reacheszero. The resonant capacitor voltage has a dc component equal to

$\frac{V_{in}}{3}$

a small ac component. In me second interval (T_(sw)-T_(res)), shown inthe second graph (b), the switches S_(W2), S_(W2a), S_(2b) and S_(2c)are turned “on” with zero current. The inductor L_(r) and capacitorC_(rb) are connected to the output terminal V_(out). Inductor L_(r) andcapacitor C_(rb) start resonating and the energy in capacitor C_(rb) istransferred to the output terminal V_(out). Similar to previous intervalthe switches S_(W2a), S_(2b) and S_(2c) (shown by dotted line) areturned “off” before half the resonant period and diode connected inparallel across switch S_(W2a) starts conducting.

In graph (c), lower inductor ripple current (I_(Lr)) converter 1500B maybe by virtue of the inductor current (I_(Lr)) being in the samedirection compared to what may be a larger bi-directional inductorripple current (I_(Lr)) of converter 1500A for example. Inductor ripplecurrent (I_(Lr)) of converter 1500B is positive.

Graph (d) shows for converter 1500B, three plots of the input voltageV_(in) (shown by wider spaced dotted line), the output voltage V_(out)(shown by narrower spaced dotted line) and the voltage across capacitorsC_(ra) and C_(rb) (shown as solid line). Graph (d) shows the buckoperation of converter 1500B such that the output voltage (V_(out)) islower and negative and/or inverted compared the input voltage (V_(in))by virtue of a conversion ratio of a third.

Reference is now made to FIGS. 16 a and 16 b , which show respectiveinverting converters 1600A and 1600B with conversion ratios of a third,according to illustrative embodiments. Common to both FIGS. 16 a and 16b is a series connection of switches S_(W1), S_(W2), S_(W1a) andS_(W2a). Capacitor C_(in) connects between terminal V_(in) and terminalG. Capacitor C_(out) connects between terminal V_(out) and terminal G.Terminal V_(in) connects to switch S_(W1) and terminal V_(out) connectsto switch S_(W2a).

Specifically, for converter 1600A, inductor L_(r) connects between thepoint where switch S_(W1) connects to switch S_(W2) and to the ends ofswitches S_(2b), S_(3c) and capacitor C_(ra). Terminal G also connectsto the point where switch S_(W2) is connected to switch S_(w1a).

Specifically, for converter 1600B, the point where switch S_(W1)connects to switch S_(W2) connects to the ends of switches S_(2b),S_(3c) and capacitor C_(ra). Inductor L_(r) connects between terminal Gand to the point where switch S_(W2) is connected to switch S_(w1a).

Common to both converters 1600A and 1600B, the other end of capacitorC_(ra) connects to a series connection of switch S_(1b), capacitorC_(rb), switch S_(1c) and capacitor C_(rc). The body diodes of switchesS_(1b) and S_(1c) are in the opposite direction of the other switchesincluded in converters 1600A and 1600B. The other end of switch S_(2c)connects to the point where switch S_(1b) connects to capacitor C_(rb).The other end of switch S_(2b) connects to the point where switch S_(1c)connects to capacitor C_(rc). The other end of capacitor C_(rc) connectsto the point where switch S_(W1a) connects to switch S_(W2a). SwitchS_(2d) connects between terminal V_(out) and the point where capacitorC_(rb) connects to switch S_(1c). Switch S2 e connects between terminalV_(out) and the point where capacitor C_(ra) connects to switch S_(1b).

Reference is now made to FIG. 16 c , which shows four graphs (a), (b),(c) and (d) of voltages and current versus time according toillustrative embodiments. The four graphs (a), (b), (c) and (d) are forstep-down (buck) converter 1600B with conversion ratio of a third. WhenS_(W1), Soria, S_(1b) and S_(1c) are turned “on” in a first interval,inductor L_(r) and capacitors C_(ra), C_(rb) and C_(rc) connected inseries by switches S_(1b) and S_(1c) resonate. Current I_(Lr) startsvarying sinusoidally and energy is transferred to resonant capacitorsC_(ra), C_(rb) and C_(rc) during the first interval (T_(res)). In graph(a), switches S_(W1a), S_(1b) and S_(1c) (shown by dotted line) areturned “off” before half the resonant period after which switch S_(W1)(shown by solid line) is turned “off”. The diode connected in parallelto switch S_(W1a) starts conducting the inductor current I_(Lr) and theresonance stops when the inductor current I_(Lr) reaches zero. Theresonant capacitor voltage has a dc component equal to

$\frac{V_{in}}{3}$

and a small ac component. In the second interval (T_(sw)-T_(res)), shownin the second graph (b), the switches S_(W2), S_(W2a), S_(2b), S_(2c),S_(2d) and S_(2e) are turned “on” with zero current. The inductor L_(r)and capacitor C_(rc) are connected to the output terminal V_(out).Inductor L_(r) and capacitor C_(rc) start resonating and the energy incapacitor C_(rc) is transferred to the output terminal V_(out). Similarto the previous interval, the switches S_(W2a), S_(2b), S_(2c), S_(2d)and S_(2e) (shown by dotted line) are turned “off” before half theresonant period and diode connected in parallel across switch S_(W2a)starts conducting.

In graph (c), lower inductor ripple current (I_(Lr)) converter 1600B maybe by virtue of the inductor current (I_(Lr)) being in the samedirection compared to what may be a larger bi-directional inductorripple current (I_(Lr)) of converter 1600A for example. Inductor ripplecurrent (I_(Lr)) of converter 1600B is positive.

Graph (d) shows for converter 1600B, three plots of the input voltageV_(in) (shown by wider spaced dotted line), the output voltage V_(out)(shown by narrower spaced dotted line) and the voltage across capacitorsC_(ra) and C_(rb) (shown as solid line). Graph (d) shows the buckoperation of converter 1600B such that the output voltage (V_(out)) islower and negative and/or inverted compared the input voltage (V_(in))by virtue of a conversion ratio of a third.

Reference is now made to FIG. 17 , which shows a block diagram 1700 ofan algorithm to determine a switching frequency (f_(SW)) for a converterdescribed above, according to illustrative embodiments. The algorithmmay be implemented for the converters described above since tolerancesof the resonant capacitor(s) (C_(r), C_(ra), C_(rc), C_(rd) and C_(re))and resonant inductor (L_(r)) may cause the resonant frequency (f_(res))of the converter to be different from the initially designed value.Operating at a higher or lower switching frequency (f_(SW)) can causenon-zero current switching and increase the total losses in theconverter. To compensate for the tolerances of the components in theconverter, the resonant inductor current (I_(Lr)) is sampled at risingedge of the switching signal S_(g1) by use of samplers 1705 and sampler1707 via the unity (|u|) modulus 1703 of the resonant inductor current(I_(Lr)). When the switching frequency (f_(SW)) is equal to resonantfrequency (f_(res)) via subtractor 1709, the magnitude of the current iszero. A proportional integral (PI) controller 1715 may be implemented tovary the switching frequency (f_(SW)) to make the magnitude of currentzero as required. To determine the sign 1711 of the error input fromerror unit 1713 to PI controller 1715, a second current sample ismeasured after a delay (T_(d)) (200 ns by way of non-limiting example)from delay 1701. Based on the current samples of samplers 1705/1707,magnitude of the error 1713 is determined in order to obtain the correctswitching frequency (f_(SW)) out the output of adder unit 1717.

Reference is now made to FIG. 18 a , which shows a bidirectional AC toAC converter 1800, according to illustrative embodiments. Converter 1800may be similar to the DC-to-DC converters described above and may beextended to facilitate the operation for AC to AC conversion. CapacitorC_(in) connects across single phase AC input voltage V_(inAc) atterminals Live (L) and Neutral (N). A series string of bi-directionswitches connects between capacitor Cin at terminal L and output Live(L) terminal Vout. Output capacitor Cout connects across terminal Live(L) terminal Vout and terminal Neutral (N).

The series string of bi-directional switches BDSW includes, for example,switch S_(W1d) with body diode connected in parallel across switchS_(W1d), the cathode of switch S_(W1d) connects one end of switchS_(W1d). The anode of switch S_(W1d) connects to the other end of switchS_(W1d) and to one end of switch S_(W1r) and the anode of the body diodeof switch S_(W1r). The other end of switch S_(W1r) connects to thecathode of the body diode of switch S_(W1r). As such, the series stringof bi-directional switches BDSW connects the cathode of switch S_(W1d)to the live (L) terminal of AC source V_(inAc), the cathode of switchS_(W1r) connects to the cathode of switch S_(W2d), the cathode of switchS_(W2) r connects to the cathode of switch S_(W1ad), the cathode ofswitch S_(W1ar) connects to the cathode of switch S_(W2ad) and thecathode of switch S_(W2ar) connects to terminal V_(out). Inductor L_(r)connects between neutral (N) and the point where the cathode of switchS_(W2) r connects to the cathode of switch S_(W1ad). Capacitor C_(r)connects to the point where the cathode of switch S_(W1r) connects tothe cathode of switch S_(W2d) and the point where the cathode of switchS_(W1ar) connects to the cathode of switch S_(W2ad).

Reference is now made to FIG. 18 b , which shows three graphs (a), (b)and (c) of voltages and current versus time according to illustrativeembodiments. Converter 1800 may be similar to the DC-to-DC convertersdescribed above and may be extended to facilitate the operation for ACto AC conversion. In particular converter 1800 may be most similar toconverter 1100 b shown in FIG. 11 b since the bidirectional switchesBDSW provide two directions of switching in a unity mode of invertingconversion for respective positive and negative cycles of AC sourceV_(inAc) as shown in graph (b). Graph (b) shows the inverted unityoutput voltage on terminal V_(out). In other words, strings of switchesSW1 d, SW2 d, SW1 ad, SW2 ad and switches SW1 r, SW2 r, SW1 ar, SW2 arconvert in the same way as converter 1100 with its string of switchesdescribed above with respect to FIGS. 11 c and 11 d but instead forrespective positive and negative cycles of AC source V_(inAc). As suchinductor current I_(Lr) as shown in graph (a) is one positive directionfor the negative cycle of AC source V_(inAc) and is one negativedirection for the positive cycle of AC source V_(inAC). Voltage acrosscapacitor C_(r) is shown in graph (c).

Converter 1800 may be similar to the DC-to-DC converters described abovein that inductor L_(r) is located and/or connected betweenneutral/ground and midpoint of a series connection of serially connectedswitches. Converter 1800 may be similar to the DC-to-DC convertersdescribed above in that inductor L_(r) is connected in series withcapacitor C_(r) and may be connected across two switches in a string ofserially connected switches. Converter 1800 may be similar to theDC-to-DC converters described above in that a multi-leg version similarto converter 1100C in FIG. 11 e and/or converters 1100A/B, 1200A/B,1300A/B, 1400A/B, 1500A/B, and 1600A/B may be constructed. As such themulti-leg version similar to converter 1100C in FIG. 11 e may beconnected and/or operated to provide a single-phase (V_(inAc)) AC buckand/or boost function that minimizes ripple current in capacitors C_(in)and C_(out).

Further, a multi-leg version similar to converter 1100C in FIG. 11 e maybe connected and/or operated to provide a single phase to three phaseoutput and/or with a phase by phase AC buck and/or boost function thatminimizes ripple current in capacitors C_(in) and C_(out). AC to ACconverter 1800 may be used to implement DC-to-DC converters and DC-to-ACconverters such as DC-to-DC converter 302, DC-to-AC converter 303 andother DC-to-DC and DC-to-AC converters described above. In sum, an AC toAC converter 1800 may be similar to the DC-to-DC converters describedabove that may include FIGS. 11 a-16 b so as to provide lower inductorripple currents (I_(Lr)) by virtue of relocating/re-connecting inductorsL_(r) that may result in inductors L_(r) with lower inductor volumeand/or utilization of one or more legs that may lower ripple currentratings for capacitors C_(in) and C_(out).

It is noted that various connections are set forth between elementsherein. These connections are described in general and, unless specifiedotherwise, may be direct or indirect; this specification is not intendedto be limiting in this respect. Further, although elements herein aredescribed in terms of either hardware or software, they may beimplemented in either hardware and/or software. Additionally, elementsof one embodiment may be combined with elements from other embodimentsin appropriate combinations or sub-combinations. For example, theswitch(s), sensor(s), power source(s), storage element(s), andinterconnections of one embodiment may be combined with similar elementsof another embodiment and used in any combination or sub-combination.Also, power sources shown in the Figures may be alternating current (AC)sources and multi-converters connected thereto may serve as AC-to-DCconverters such as rectifiers and/or switched mode power supply, forexample. One skilled in the art will recognize that the variousembodiments detailed above may be combined in suitable combinations andthat portions of the embodiments may be unitized in varioussub-combinations.

According to a first illustrative embodiment, there is provided anapparatus, which includes a DC-to-AC converter comprising a firstterminal and a second terminal. The apparatus also includes a DC-to-DCconverter comprising a third terminal. The DC-to-AC converter may beconfigured to receive a DC input voltage from a DC power source, and toproduce a first alternating output voltage at the first terminal, and asecond alternating output voltage at the second terminal. The DC-to-DCconverter may be configured to receive a DC input voltage from the DCpower source.

With respect to the first illustrative embodiment, the DC-to-DCconverter may be configured to step down the DC input voltage by abouthalf at the third terminal.

With respect to the first illustrative embodiment, the DC-to-DCconverter may be a charge-pump circuit.

With respect to the first illustrative embodiment, the DC-to-DCconverter may be a resonant switched capacitor circuit.

The apparatus according to the first illustrative embodiment may alsoinclude a switching device that is configured to couple the DC-to-ACconverter and the DC-to-DC converter to at least one electrical load.With respect to the apparatus that includes the switching deviceaccording to the first illustrative embodiment, the switching device maybe configured to couple a first group of electrical loads to the firstterminal and a second group of electrical loads to the second terminal,wherein a first power demand is associated with the first group ofelectrical loads and a second power demand is associated with the secondgroup of electrical loads.

With respect to the apparatus that includes the switching deviceaccording to the first illustrative embodiment, the switching device maybe configured to receive a control signal, and wherein, responsive tothe control signal, the switching device may be configured to reduce animbalance between the first power demand and the second power demand bychanging an association of at least one electrical load from the firstgroup of electrical loads to the second group of electrical loads orfrom the second group of electrical loads to the first group ofelectrical loads.

According to a second illustrative embodiment, there is provided anapparatus that includes a DC-to-AC converter. The DC-to-AC converter mayinclude a first output, a second output having 120-degree phasedifference from the first output, and a third output having 120-degreephase difference from the first output and 120-degree phase differencefrom the second output. The apparatus further includes a DC-to-DCconverter comprising a fourth output. The DC-to-AC converter may beconfigured to receive a DC input voltage from a DC power source. Thefirst output, the second output and the third output may be configuredto output AC voltages having about a same frequency and a same voltageamplitude. the DC-to-DC converter may be configured to receive a DCinput voltage from the DC power source.

With respect to the second illustrative embodiment, the DC-to-DCconverter may be configured to step down the input voltage by about halfat the fourth output.

With respect to the second illustrative embodiment, the three outputs ofthe DC-to-AC converter may be configured to be coupled to three-phaselines of a three-phase power system, and the fourth output may beconfigured to be coupled to a neutral line of a three-phase powersystem.

According to a third illustrative embodiment, there is provided a methodthat includes receiving, by a DC-to-AC converter comprising a firstterminal and a second terminal, a DC input voltage provided by a DCpower source. The method also includes receiving, by a DC-to-DCconverter comprising a third terminal, the DC input voltage provided bythe DC power source. The method further includes producing, by theDC-to-AC converter at the first terminal, a first alternating outputvoltage. The method still further includes producing, by the DC-to-ACconverter at the second terminal, a second alternating output voltage.The method also includes producing, by the DC-to-DC converter at thethird terminal, a stepped down DC output voltage with respect to the DCinput voltage.

With respect to the third illustrative embodiment, the DC-to-DCconverter may be a charge-pump circuit.

With respect to the third illustrative embodiment, the DC-to-DCconverter may be a resonant switched capacitor circuit.

The method according to the third illustrative embodiment may furtherinclude selectively coupling, via a switch, the DC-to-AC converter andthe DC-to-DC converter to at least one electrical load.

According to a fourth illustrative embodiment, there is provided amethod that includes receiving, by a DC-to-AC converter comprising afirst output, a second output having 120-degree phase difference fromthe first output, and a third output having 120-degree phase differencefrom the first output and 120-degree phase difference from the secondoutput, a DC input voltage provided by a DC power source. The methodalso includes receiving, by a DC-to-DC converter comprising a fourthoutput, the DC input voltage from the DC power source. The methodfurther includes outputting, by the DC-to-AC converter on the firstoutput, the second output and the third output, AC voltages having abouta same frequency and a same voltage amplitude. The method still furtherincludes outputting, by the DC-to-DC converter on the fourth output, astepped down DC voltage with respect to the DC input voltage.

With respect to the fourth illustrative embodiment, the DC-to-DCconverter may be a charge-pump circuit.

With respect to the fourth illustrative embodiment, the DC-to-DCconverter may be a resonant switched capacitor circuit.

The method according to the fourth illustrative embodiment may furtherinclude selectively coupling, via a switch, the DC-to-AC converter andthe DC-to-DC converter to at least one electrical load.

1. An apparatus comprising: an input terminal, a reference terminal, andan output terminal; and at least one series string of switches connectedbetween the input terminal and the output terminal, wherein each of theat least one series string of switches comprises at least: a firstswitch connected between the input terminal and a first common terminal;a second switch connected between the first common terminal and anintermediate node; a third switch connected between the intermediateterminal and a second common terminal; and a fourth switch connectedbetween the second common terminal and the output terminal; at least onefirst capacitor connected between the first common terminal and thesecond common terminal; an inductor connected between the intermediatenode and the reference terminal; and a controller configured to causethe apparatus to output a voltage between the reference terminal and theoutput terminal by switching, at a first frequency, the first, thesecond, the third, and the fourth switches of the at least one seriesstring of switches, wherein the switching includes: during each firsthalf period of the first frequency, turn on the first and the thirdswitches, and turn off the second and the fourth switches; and duringeach second half period of the first frequency, turn on the second andthe fourth switches, and turn off the first and the third switches. 2.The apparatus of claim 1, wherein each of the at least one series stringof switches is configured to output the voltage by converting inputpower between the input terminal and the reference terminal to outputpower between the output terminal and the reference terminal; andwherein the converting is based on stepping down, stepping up, orinverting the input power.
 3. The apparatus of claim 1, furthercomprising: a second capacitor connected across the input terminal andthe reference terminal; and a third capacitor connected across theoutput terminal and the reference terminal.
 4. The apparatus of claim 1,wherein the apparatus comprises N number of series strings of switches;and wherein the controller is further configured to operate each of theN number of series strings of switches at a phase shift of 360°/N withrespect to at least another of the N number of series strings ofswitches.
 5. The apparatus of claim 4, wherein each of the N number ofseries strings of switches outputs 1/N of output power between theoutput terminal and the reference terminal.
 6. The apparatus of claim 1,wherein the at least one series string of switches comprises multipleseries strings of switches; and wherein each of the multiple seriesstrings of switches is configured to have a current flow, via theinductor of the each of the multiple series strings of switches, in asame direction.
 7. The apparatus of claim 1, further comprising: aplurality of diodes, wherein each of the plurality of plurality ofdiodes is connected in parallel to one of the first, the second, thethird, or the fourth switch; wherein each of the plurality of diodes areis configured to have current flow in a same direction.
 8. The apparatusof claim 7, wherein each of the plurality of diodes is integrated withinthe one of the first, the second, the third, or the fourth switch. 9.The apparatus of claim 1, wherein each of the first, the second, thethird, and the fourth switches comprises a bi-directional switch. 10.The apparatus of claim 9, wherein the voltage is a single-phasealternating current (AC) voltage of a second frequency different fromthe first frequency.
 11. The apparatus of claim 10, wherein theapparatus is configured to output the single-phase AC voltage by:receiving a second single-phase AC voltage between the input terminaland the reference terminal, wherein the single-phase AC voltage and thesecond single-phase AC voltage have opposite phases; and converting,based on the switching, the second single-phase AC voltage to thesingle-phase AC voltage.
 12. The apparatus of claim 1, wherein thevoltage is a direct current (DC) input voltage; and wherein a DC outputvoltage between the input terminal and the reference terminal and the DCinput voltage have opposite phases.
 13. The apparatus of claim 1,wherein the controller is further configured to, during each first halfperiod of the first frequency, turn on, at substantially a same time,the first and the third switches of the at least one series string ofswitches.
 14. The apparatus of claim 13, wherein the controller isfurther configured to, during each first half period of the firstfrequency, turn off the third switch of the at least one series stringof switches prior to turning off the first switch of the at least oneseries string of switches.
 15. The apparatus of claim 13, wherein thecontroller is further configured to switch, under zero-currentconditions, the first switch of the at least one series string ofswitches.
 16. The apparatus of claim 1, wherein the controller isfurther configured to: determine a resonant frequency of a currentflowing through the inductor; and adjust, based on the resonantfrequency, the first frequency.
 17. The apparatus of claim 1, furthercomprising: a direct current (DC)-to-alternating current (AC) convertercomprising a first AC output terminal and a second AC output terminal;wherein the input terminal and the reference terminal are configured toreceive a DC input voltage from a DC power source and provide a DCoutput voltage to the DC-to-AC converter; and wherein the DC-to-ACconverter is configured to: receive the DC input voltage from the DCpower source and the DC output voltage; and produce a first AC outputvoltage at the first AC output terminal, and a second AC output voltageat the second AC output terminal.
 18. The apparatus of claim 17, whereinthe DC output voltage is substantially half of the DC input voltage. 19.The apparatus of claim 17, wherein the apparatus is configured to:provide, between the reference terminal and the output terminal, the DCoutput voltage to a plurality of groups of electrical loads comprising afirst group of electrical loads and a second group of electrical loads;and regulate the DC output voltage by supplementing or absorbing acurrent difference between a current associated with the first group ofelectrical loads and a current associated with the second group ofelectrical loads.
 20. The apparatus of claim 19, wherein the DC-to-ACconverter is further configured to: provide, via the first AC outputterminal of the DC-to-AC converter, the first AC output voltage to atleast the first group of electrical loads from the plurality of groupsof electrical loads, and provide, via the second AC output terminal ofthe DC-to-AC converter, the second AC output voltage to at least thesecond group of electrical loads from the plurality of groups ofelectrical loads.